The present invention concerns optical scanning of an image and pertains particularly to detecting the boundaries of a scanned image.
Optical scanners allow images to be scanned into a computer system for modification and use. In addition, scanners are used when implementing such things as faxes and copiers. See for example the HP OfficePro 1150C printer (available from Hewlett Packard Company, having a business address of 3000 Hanover Street, Palo Alto, Calif. 94304), which functions as a color printer, a copier and a scanner, or the HP OfficeJet 570 printer (also available from Hewlett Packard Company), which functions as a color printer, a fax, a copier and a scanner.
It is sometimes desirable when scanning an image to determine a minimal rectangular bounding box within which that image lies. This is particularly useful when performing a copy of an image because the use of a minimal rectangular bounding box can limit the amount of processing needed to reproduce the image. In addition, the use of a minimal rectangular bounding box can be used in the implementation of various features on a copier.
Bounding boxes can be defined, for example, by performing a one bit black and white prescan of an image. The bounding box is then specified by the leftmost, rightmost, topmost, and bottommost black pixels. The disadvantage in this solution is that it has no ability to reject dust particle marks. If the algorithm is modified so there is the ability to reject dust particles marks, this can result in the rejection of marks from the actual image which should be used to help define the bounding box.
Other algorithms have used very elaborate means to define edges, classify and/or extend subregions, or perform other complex calculations. These algorithms have the disadvantage of requiring extensive CPU processing or large data arrays to process the prescanned image.